Abstract:The relationship between characteristics of genome size (ploidy, chromosome number, C-value and GS) and seed (1000-seed weight, oil content and protein content), which were searched from Plant C-value Database and Seed Mass Information Database, was analyzed by ANOVA and regression model for 282 species in Poaceae. The results showed that the C-value and 1000-seed weight changed from 0.35 to 19.7 pg and from 0.05 to 252 g, and the means were 4.14 pg and 7.1 g, respectively. With the ploidy increasing, the C-values increased significantly from diploid to octoploid, but the GS and mean DNA content of each chromosome decreased significantly from diploid to hexaploid (p<0.05). The C-value of Bromus and Festuca showed similar change as Poaceae, but GS did not decrease significantly. Linear correlation analysis showed that there were significantly positive correlations between C-value and ploidy, number of chromosome, GS and mean DNA content of each chromosome, but there were significantly negative correlations between GS and number of chromosome and ploidy (p<0.01). Regression analysis showed that there was significantly positive correlation between GS and 1000-seed weight (p<0.01), but there was almost no correlation between C-value and 1000-seed weight. There was significantly negative correlation between C-value and oil content of seeds, but no correlation between C-value and protein content. There was higher species in Poaceae increased their C-values primarily by ploidy doubling in the phylogeny and evolution history, but at the same time, the C-value was stopped to increase infinitely through reducing GS and mean DNA content. This study will give some reference to study the relationship between genome size evolution and plant phylogeny.